[ARCHIVED] Partnered Sims turn into siblings/family relationships

I'm having this problem too currently, but my problem started when I used MCCC to accidentally make my female vampire Sim the sister of Alexander Goth. I deleted their relationship afterwards, but it keeps putting them as brother and sister, even though they're husband and wife. And their kids keep getting changed to brother/sister/cousins. I have since deleted the relationships between my female Sim and Alexander Goth about 5 times now. I even deleted a bugged version of the female Sim and added a new version of her to the game, but she still ends up being the sister of Alexander Goth, even though she is his wife. I should also note that everyone in my household are vampires, I have never played with a spellcaster in this save, and I have not duplicated/cloned any Sims. The problem seems to exist in both the game itself and MCCC, as it started happening in my game after I accidentally made my female Sim and Alexander Goth brother and sister using MCCC. And since then, the game continuously seems to think they are brother and sister, even though they are married to one another/have children with one another.

Edit: And I only accidentally made them brother and sister using MCCC to begin with, because my female Sim would not romance Alexander Goth at all (the only option she had under romance was "Offer Massage"). I do use mods in my game, but seeing as this problem happens to people who don't even use mods, I don't think this is mod-related; I think it's a game bug and a game-breaking bug at that. EA, you need to fix this ASAP!